The object of this study is to determine variables associated with therapy-success of a cognitive behavioral self help intervention for insomnia. In this study all participants receive an online self-help CBT manual consisting of information (psycho-education) about sleep and cognitive-behavioural exercises. Adult persons with insomnia will be invited via a popular scientific website to fill out online questionnaires. Participants will be measured 4, 16, and 40 weeks after intervention with the same questionnaires.